text:
Are there any proposals to continuously stream "black box" data?
After an aircraft incident, finding the black box is important to investigate the causes, because it contains a lot of valuable recorded data.  The process of locating this can take a lot of time, and perhaps in some cases it will not be found at all, or deliberately sabotaged.  Both problems could be mitigated by continuously streaming flight data through a satellite uplink — or, if there is no coverage, buffer the data until there is.
Do any aircraft do so, or are there any serious proposals to start doing so in the future?  What would be the largest obstacles?

cost of the satellite uplink itself and the bandwidth taken up by the hundreds of flights in the air at any one moment

@ratchetfreak  Cost is no longer an excuse.  UPS can track information on it's $100,000 trucks via a satellite connection.  They do it because they can use the data to save money.  Even a retail prices for iridium phones, it would be worth it for a $150,000,000 plane.

See this answer for links to Inmarsat and IATA proposals.

@DavidNehme UPS doesn't use a satellite connection to track truck but the cell phone network; a 140 char text every minute to a central server using a cell phone is cheaper than getting a 2 way satellite uplink

@ratchetfreak It is also a lot lighter.

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text:
Why not tow aircraft instead of single-engine taxi?
To save costs, budget airlines could potentially eliminate the single-engine taxi that is standard.
Companies are looking into things like electric motors on the wheels of airliners for taxi, which could be powered by the APU, using much less fuel than even a single-engine taxi.
But why not just tow all of them using existing towing equipment?

The related post 'Does it make sense towing airplanes to the head of airstrip by electric means?' asks for electric technology (internal or external), this one asks about using existing technology.

Does one such system require FAA Authorisation and is it more costly? in terms of electricity for / capital for solar panels and night time batteries for Charging towing vehicles if they are electric or net fuel use per tow in the case of combustion engine vehicles?

why the world isn't as perfect as it could be? because change takes time and money

Voting to leave open. What's on that other thread is mostly discussing "cool innovative new ideas" rather than just using the tugs that exist now. One post there talks about a tug being used, but doesn't address the "why aren't they used more" aspect of the question. I don't think this question is answered there, and I think it of sufficiently distinct flavor to leave open as-is.

@RalphJ All of the answer etc. and it was still closed... why I dislike SE these days

That would mean tugs dragging aircraft slowly round the taxiways, increasing delays.  Then the tug would have to be released from the aircraft while it holds just short of the runway, Then the tug would have to clear the runway, introducing delays, and make its way back to the ramp to tow another aircraft, introducing congestion and delays.

Towing is much slower than taxiing.
When taxiing, you have on the order of 25 MW available, and taxi speeds seem to be 55 km/h.
Towing vehicles have on the order of 500 kW, and towing speed about 5 km/h.

“have 25 MW available” – how do you arrive at this number? Even with the full 430 kN a Trent XWB can offer (I daresay it won't during taxiing, but let's leave that out), you can at 55 km/h extract at most 6.57 MW for kinetic purposes.

"on the order of " indicates I'm not quoting exact numbers, merely indicating an order of magnitude. The important point is that the aircraft's engines are two orders of magnitude more powerful than a tow tractor.

Well I daresay it's only one order of magnitude realistically speaking, but suppose the point stands nevertheless. But I don't think this is really the reason why towing isn't used – it would certainly also be possible to design towing vehicles with a few megawatts of power, but probably not safe or economic to use them on airports.

@leftaroundabout: Unless you're towing with jets your tow vehicle will have to weigh too much to be remotely reasonably controlled as it's limited by tractive effort rather than motive power.

@Joshua How about we take some of those plane engines and mount them on the tow trucks? :P

Its slow to tow. Even with a towbarless (which can tow faster) it is not ideal.
Danger of miscommunication/slow communications.
Most airliners cannot be towed with 2 engines or more running as the idle thrust is high. Therefore at least one may need to be started just before takeoff. This is not good for engines going from cold to take-off thrust in a few minutes. Also a no-start or fault on start will require a tow back to the gate.
A taxi to runway in a large airport would take half an hour to an hour. A push-pack..? 10-15 minutes at the most? Towing to the take-off points will require a big increase in the number of pushback equipment.

Having said that there have been cases where aircraft have been towed into position on or near the entry point of the runway. One case was United's first non-stop from New York (or was it Newark) to Hong Kong back in the late 90s. Aircraft was towed and I believed lined up with the runway to ensure the flight started off with max fuel.
Another scenario would be if the entry into the runway was not at the very start and the turning pan was either not existent or not suitable. To get every inch of runway the aircraft may be towed onto and backed-up to the start of the runway.

"A taxi to runway in a large airport would take half an hour to an hour." Can you give an example or two of airports where this might be the case in reasonable traffic conditions? I'm quite certain it would not be the case at Amsterdam Schiphol, at least, and that likely qualifies as a pretty large airport by most reasonable peoples' standards.

@aCVn: Doesn't taxiing to/from one particular runway at Schiphol already take that long, even with aircraft taxiing under their own power?

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sort: votes


text:
Is the Airbus Beluga's safety record comparable with the record of other Airbuses?
Upon first sight, to the uneducated eye, the Airbus Beluga looks incredibly 'un-aerodynamic'. Is the Beluga just as safe as other Airbus models?

It might be even safer. No hull loss.

I don't see how you can get a reduction on allowable (technical) risk from the certification authorities for a large aircraft. And @vasin1987 has said that there have been no hull losses.

@jjack The Beluga is certified as a restricted category aircraft. As EASA puts it, "This is intended for aircraft that cannot comply with all applicable airworthiness requirements because they are specifically designed for a special purpose..."

What are you worried about happening?

A Beluga apparently had a cockpit wiring fire yesterday... The Beluga TCDS does note restricted conditions about stalls, operational speeds, gust tolerance, and a stick pusher (not present on the base model), so the question whether there are aerodynamic compromises is probably yes.

@zeta-band Well... an accident I guess! :)

OK, @Cloud, what did you do?

@Sean What do you mean? I didn't die on the flight so that's a bonus... :)

There's a history of oversize airplanes for transport. One of the earliest was the Pregnant Guppy and its successor the Super Guppy

By NASA/Tom Tschida - http://www.nasa.gov/centers/dryden/multimedia/imagegallery/Guppy/EC00-0212-2.html (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=32895741
Boeing operates its own variant, the Dreamlifter

By scott wright (originally posted to Flickr as n780ba) [CC BY 2.0 ( http://creativecommons.org/licenses/by/2.0 )], via Wikimedia Commons
To my knowledge, none of these (including the Beluga) have had any safety incidents (although the Dreamlifter did once land at the wrong airport). I'm not sure if there's any conclusions on safety to draw from, however, as there aren't a lot of these around, as they primarily transport large materials (like aircraft parts).

There's definitely been Beluga safety incidents. I do remember something falling off it 10+ years ago.

The Beluga, or other bulk-freight carriers, such as the Guppy variants or the Dreamlifter, are as aerodynamic as they can be, regarding the contrains on cargo volume. So, they are unusually shaped/large, yet they are not un-aerodynamic.
As for the safety record, there is only a small number of Belugas. So, the safety statistics is not comparable to a large-number type, e.g. A300.
Furthermore, the per-plane, per-year mileage is much larger for the common passenger carriers that for the bulk-cargo carriers. So, a single A300 clocks much more miles in a year than a Beluga.
To conclude, statistics becomes more and more significant the larger the involved sample is. Statisticians might argue, whether a sample of 5 (hulls, in the case of the Belugas) is a sample at all (strictly statistically/mathematically speaking).

To add, all belugas owners can certainly do prime maintenance on their air carriers and give prime training to the pilots. Both major factors in accident prevention.

I wouldn't be surprised if a single A300 clocks more miles each year than the entire Beluga fleet.


text:
To flap or not to flap?
I am learning to fly an Ikarus-C42. The instructor I have recommends to all students that they land without flaps, because it is less to think about and because it gives you more airspeed, thus less chance of stalling or losing control on approach.
Now, I'm not one to second guess someone much more experienced than me, but I do have to ask - is this truly best practice?
I have conducted some reading on the subject and it seems that not using flaps and the consequent high speed landings performed by many students is one of the main reasons for the high incident rate that involve overshooting runways (not to mention the excessive wear on the brakes). Additionally, it doesn't seem to prep you well for the 'real world'. I can't imagine telling your F.O on a 737 'Don't worry about flaps today, it's too much to think about' :D

I think at least one answer should say "If offered the choice between doing what your instructor says, and what some guys on the internet say, go with your instructor."

@DJClayworth I think mine comes fairly close. I didn't use those exact words, but the sentiment is there.

Glad to see this question asked. Even as a new glider student, I already found the landing procedure overwhelming: turn, speed, trim, flap, brake, watch for runway... all at the same time.

Remember not to get too close the sun! :)

The "thus less chance of stalling" is not a valid rationale (but workload is). With flaps, the stall speed is lower, so by flying slower you are not closer to stall. The approach speeds are selected with the stall margin as a primary factor, so if you obey the prescribed speeds you should be equally safe in this regard.

You don't say which variant you're flying, but the C42B is perfectly capable of both taking off and landing with zero flaps on a reasonable-length runway. I've done it on several occasions with huge margin even for touch-and-gos on my home field's 1300 m asphalt runway. You do need to adjust the angle of attack (via pitch), but if you're flying the airspeed you'll basically be doing that anyway, so no big deal.
Extending flaps give you better flying characteristics at low airspeed, but increases drag. If you're flying the approach at reasonably high speed, then you likely don't particularly need the extra lift, and in fact it might even be detrimental especially once you're wheels on runway and trying to slow down. With flaps extended, you also need to monitor your airspeed more closely to make sure you aren't exceeding VFE.
On the flip (flap?) side, the C42 flaps lever manipulates the flaps directly -- it's just a cable going through the fuselage. Any time you're handling the lever, you are fighting directly against the airflow around the wing, with no help from e.g. elevator trim, let alone hydraulics or even electrics. I know that the effects of this came as a bit of a surprise for me the first few times I retracted flaps in flight; it's very easy to end up with a rough flaps retraction if you aren't prepared for the force involved.
You're supposed to be flying the airplane all the way to the ground, and only bleed off the flying airspeed very late during the landing, in the flare when you should end up at stall speed with the wheels just barely above the runway.
It's possible that your instructor feels that the added complexity of also handling the flaps lever (and the resultant drag changes) simply may risk being overwhelming at first. It's not like there isn't already a lot going on during a standard traffic pattern coming in to land; there's airspeed, altitude, auxiliary pump, carb heat, scanning for traffic, radio communications, keeping good tabs on your position relative to the runway, lining up for final approach mind the wind, making sure your turns are coordinated, during crosswind landings the final turn to align the airplane (as opposed to the direction of travel) with the runway, ...
Your instructor likely has a plan for how to introduce the use of flaps during landing; you are most likely going to need them by the time you're doing short-field work, if not before. You also can, and should, discuss with your instructor anything where you don't feel that you understand the instructor's rationale. Asking strangers on the Internet for advice is fine, and can provide additional insight (which can be quite valuable!), but should never be a replacement for asking your instructor.

high incident rate that involve overshooting runways

If you're too far along the runway to land safely, just go around and make another attempt. (Landing long is fine, just annoying if you need to taxi all the way back; overshooting the runway is not.) It's good practice for everything except the flare, braking and taxiing, and it's good practice for go-around procedures. I've made the decision to go around in situations that very likely were perfectly fixable (things like being too high on final, or drifting to the side while still a moderate distance out on final) but I am of the opinion that it's better to go around and do it right, than try to press on when things are stacking up against you, especially if you're new. With experience, you'll learn what can be fixed in-place and what truly warrants a go-around.
Just make sure you tell the instructor what you're doing. Crew resource management isn't a big focus in single-pilot light aircraft, since you'll mostly be flying by yourself and certainly a lot of the time without another pilot in the other seat, but I find it's a good idea to follow the general principles anyway.

Additionally, it doesn't seem to prep you well for the 'real world'. I can't imagine telling your F.O on a 737 'Don't worry about flaps today, it's too much to think about' :D

I know you added a smiley, but it's no joking matter. Don't treat, or think of, the C42 like a commercial jetliner. Don't think learning to fly a C42 will allow you to just drop into the cockpit of a jetliner (even a realistically simulated one) and fly the latter. It isn't, it will never be, it won't, and the C42 handles quite differently from the big iron. That doesn't make the C42 any less "real world".

Thankyou for the answer, much appreciated. The (flap?) side made me laugh.

It's an unusual practice but, in view of the Ikarus's very light control forces combined with a heavy and awkward flap lever, I am going to guess that the instructor has found that students have difficulty controlling the airplane's pitch and trim while manhandling the flap handle and it's less grief during initial training to simply leave flaps out of it until the student's skill progresses.  The very light wing loading and small flap area means there is not a huge difference in flaps up flaps down performance, so it's not so big a deal compared to say a 152, where landing flapless is considered a more advanced exercise.
Their use will in introduced in a few lessons.

The Ikarus C42 is much lighter than a comparable Cessna 152, with a much lower stall speed, even with no flaps.  If there is ample room to land, keeping it simple may be best for now.  However, busy instructors sometimes may miss something that is very important to you.  So, if you want to include flaps in your flying, let them know and include it next time out.  Smaller, lighter planes many times simply do not need them.

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text:
What to do if carbon monoxide is present?
Most small, single engine aircraft are fitted with non audible carbon monoxide detectors that turn black if it is present.
Carbon monoxide can incapacitate in mere seconds (and kill in minutes) depending on the ppm.
If you are cruising at 12,000 feet, that is not enough time to land.
So what should you do if you see a carbon monoxide warning (and begin to feel the effects of it)?

Those dot-style detectors aren't anywhere near as good as an electronic one, you may want to consider having a compact one in your flight bag. If you do use the dot-style ones make sure it's in date as part of your pre-flight check.

Just about the only situations where the dot-style detectors could be reasonably expected to serve any useful purpose (whether on aircraft, or anywhere else) would be when there is a slowly-forming leak which doesn't yet pose a danger.  Electronic carbon monoxide detectors with alarms and multi-year batteries have gotten so cheap I can't really see much reason not to have one.

@supercat UK Consumer magazine "Which?" reported recently that a lot of the electronic CO detectors on sale in the UK don't actually work! (or not well enough to eliminate the risk of slow CO poisoning over several hours). Cheap for a reason? Fire alarms are easy to test. Not so CO detectors.

@nigel222 Do you have a source for that? Because I've manually tested mine, which only cost about 7 euros and it works fine (tested with a cigarette).

https://www.which.co.uk/news/2018/06/the-lethal-carbon-monoxide-alarms-we-found-on-amazon-and-ebay/  and more behind the paywall.

@nigel222: The cheaper electronic alarms basically combine a dot-style detector with a photo sensor.  Such a sensor could be rendered useless by a long exposure to a low level of CO2, but any remotely decent alarm should be able to warn of that having occurred.

The first thing you're going to want to do is get fresh air into the cabin, by ensuring the vents/windows are open. This will dilute the amount of CO in the cabin and stop your symptoms getting worse - allowing you to land as soon as practical.
There is also some good information online which contains further advice:

Turn the cabin heat fully off.
Select maximum rate of fresh air ventilation to the cabin.
Open windows if the environment, flight profile and operating manual permit.
Consider using supplemental oxygen if available and if doing so would not  introduce another safety or fire hazard.
Land as soon as possible/practicable.
Inform Air Traffic Control of your concerns and intentions.
Select a leaner fuel mixture if possible.
After landing seek medical attention as soon as possible.
Before continuing the flight, have the aircraft inspected by a certified mechanic

If you're wondering about the first point, the reason is that the cabin heat is the primary way CO enters the cabin of light aircraft.

Typically most piston powered aircraft obtain their cabin heating by directing fresh (ram) air over the engine muffler (silencer). If there are any cracks, holes or poorly fitting components in the exhaust system, then CO-rich exhaust gases can enter the cabin. Engine exhaust may also enter the cabin through inadequately sealed firewalls and wheel wells etc.

If you get symptoms don't trust that they will go away quickly. With fresh air ventilation CO has a 4-6 hour half life in the blood. It binds very strongly with hemoglobin, so it takes a long time to get rid of it

Also note, that CO2 is heavier than the air and CO is lighter. CO2 tends to concentrate down and CO tends to concentrate at the top. Strong CO-hemoglobin bond - stronger than O-hem and much stronger than CO2-hem, is the killing feature here - it prevents oxygen to be absorbed in the blood. Get rid of the air around the head ASAP.

@Crowley I don't believe that the stratification of CO and air is significant with the natural air currents you get in an airplane. In fact, it's not significant with the currents in your house, which is why there's no preferred height for CO detectors.

@TomMcW Good point. The point of circulating fresh air is to not make the symptoms worse which will hopefully allow you to land. I'll reword that part of the answer.

@Crowley Oxygen is also lighter than CO2. Do you expect there to be significantly less oxygen near the floor?

@Sneftel I've written the part about CO2 just to distinguish how the two oxides behave differently.


text:
What effect does driving convictions have on a PPL?
Recently, I was driving some friends around when they started complaining that I was driving "too slow" (basically not over the speed limit). I stated that my reason for being cautious was I did not want to jeopardise my PPL / NPPL (in progress).
I would like to know however, what driving convictions actually do affect pilot licenses or get them revoked?

Related FAA questions: Can I get a pilot's license if my driver's license has been suspended? and My driver's license was suspended for not having insurance. Should I even bother to apply for a medical?

In the US, driving while under the effects of alcohol and drugs may have a adverse effect on your medical certificate.  Additionally, I have heard (from an FAA inspector) second hand that in one instance, someone who had a driver's license revoked for a large number of speeding and reckless driving circumstances, eventually had a medical certificate revoked.
Arrests, and administrative actions require reporting to the FAA Aeromedical branch within 60 days and failure to do so can not only affect a medical certificate, but also pilot certificates, instructor certificates, A&P certificates, controller certificates, etc.  The penalties for non-reporting are significant.
Addendum:  US pilots are required to make TWO reports relative to substance and alcohol issues.  Part 67 requires reporting notifications, arrest, etc. to the Aeromedical Branch. Part 61 requires a notifying Security at FAA upon conviction  or disposition.
Reference item 8 in the below FAQ which is provided for AME guidance:

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/media/SubstancesAbuseDependenceFAQ.pdf

Also, according to FAA documentation, the normal look back on substance abuse is 2 years.

For a Private Pilot, the licenses are completely separate and have absolutely no relation to each other.
In addition, there are no criminal record checks for a Private Pilot in the UK.
Things get very different when moving to commercial licenses and looking for careers.
I'm trying to find some further legislation with you - I would expect the CAA have a good amount of discretion on who it issues licenses, but any revocation could be subject to legal appeal.
Edit / Update:
I have found this wording in the ANO:

(1) Subject to article 172, the CAA or a person approved by the CAA for that purpose must grant licences of any of the classes specified in Part 1 of Schedule 8, authorising the holder to act as a member of the flight crew of a non-EASA aircraft registered in the United Kingdom, if it is satisfied that the applicant is—
(a)a fit person to hold the licence; and

Which does appear to give the CAA some leeway over who it grants licenses to. I'll try and see if there's a further definition.

Do you have a citation for the claim in this answer? I'm not in the UK, admittedly, but I am in the EU and to get my student's license had to sign a piece of paper that the CAA could do a check against the records of the police.

@aCVn Hard to cite a negative I'm afraid, though I did try and find something to the contrary. There are certainly no overt/standard Police checks that I'm aware of or that I had to go through. These checks are well defined int he UK and I have them regularly for employment - I'm ignoring things like terrorism and such which are much more complex shades of grey. I'm sure there are behind the scenes checks on watchlists

So someone with a DUI (not me by the way!) could get a private license?!

@Cloud A DUI would make it difficult to get a medical clearance. I don't know about the EU but where I'm from you have to basically go to rehab if it is a recent conviction before you can pass the medical.

@Cloud I don't know about driving under influence specifically (I suspect that would have been caught by the police check for the student certificate, if not the medical examination, in my case; don't know about the UK), but one of the questions that I distinctly do recall my AME asking (straight off the CAA form) was how much alcohol I consumed. In my case the answer to that one was a total non-issue.


text:
How does the safety record of a Cessna 152 compare to a jetliner in Europe?
I have a fear of flight and I'm working on it.
There is an airfield about 40 minutes from me and they offer flying lessons in a Cessna-152 for around 140 euros per hour. Pretty reasonable I think. So, this is my next step. But... I've only ever flown in an A320 / 737. This is because of the (approximate) very low risk of around 1 in 11 million of a fatal incident occurring.
My question is, what is the fatality rate (per million) for flights in a Cessna? I know it will be higher, I just want to know how much.
I did Google and look around, but the stats seem skewed on several sites as they include global incidents, whereas I know Europe is more tightly regulated than some parts of the world. Also, I'm not going to be performing (intentional) aerobatics, so I think we can exclude those cases as well.

Have you looked at the AOPA safety highlights for the Cessna 150/152?

@RonBeyer No, but I'm now about to. Thanks.

I can't give an answer on this, but the reasons why are informative. General aviation as a whole has a higher accident rate than commercial aviation, at least in part because of the many varied missions, some of which are inherently higher risk, like:

Microlights
Homebuilts
Cropdusting

So the statistics aren't going to be very much to go on. Additionally as you mention it varies a lot globally, and there's variations for the type of flying, time of day and other factors. Focusing down on the C152 isn't going to give you a good figure because they are an extremely popular training airplane, which is a higher risk activity.
Basically you want to know what the accident rate is for a European Cessna 152 flown in the day by an instructor pilot for non-training purposes, there just isn't any data source for that. It's going to be pretty low I would imagine.

Your last paragraph is correct, except it is for training purposes, since I will be, well training.

@Cloud you won't, not on an introductory flight like that. Sure, the instructor rated pilot is going to let you handle the controls, but don't really expect to learn anything. And he'll be constantly ready to take over.

@jwenting Sure, but I intend to make it a regular thing.

@Cloud this answer is important as it highlights that there are different categories of general aviation, each with its own risk levels rendering statistics for "Cessnas" misleading. With that in mind there are very good answers here, focusing on private operations (which, if you're paying an instructor, is not what you will be doing). https://aviation.stackexchange.com/questions/198/how-dangerous-is-flying-in-a-single-engine-plane

@Cloud in that case, just make sure you have a quality flying school that properly maintains their aircraft and has qualified instructors. In the EU, that'd be as a minimum an EASA certified ATO.


text:
How does an airplane owner correct an airplane misidentification showing up on FlightAware?
I have a friend in Pennsylvania with a plane in Pennsylvania. FlightAware is currently showing his airplane in the Bahamas, when it is not. He wants to know whom to contact to get this corrected. I'm assuming it's in some database being use by both FlightAware and FlightRadar24.

https://flightaware.com/about/contact/

Another possibility is that the database is correct, but the transponder on the aircraft in the Bahamas is using the wrong aircraft address.

Maybe it was repo'ed?  Like the tv show! Just kidding.

For the sake of it:
contact flightaware directly
https://flightaware.com/about/contact/

FlightAware says they just use data from the FAA.

I posted the same question in a Facebook page maintained by the FAA. I got a lot of possible answers:

Controller fat-fingered an N number
Person fat-fingered a number during ADS-registration
Plane is actually in the Bahamas (not the case here)
As for contacting FlightAware, one person wrote: "I had one like that, contacted Flightaware and they told me most likely ATC typed in the N number incorrectly, and nothing Flightaware can do about it."
An instructor wrote, "I was pondering something similar, and I suspect it is due to some ADS-B transmitters (like the GDL-82) having "Anonymous Mode" which allows the user to use a randomly generated ADS-B identifier. This theoretically reduces "Big Brother's" ability to track and individual. My guess is that the randomly generated identifier accidentally collides with a real one. Check out my student's plane that magically teleported from the PNW to SOCAL and back just before Christmas"
A pilot wrote, "It'll take care of itself. I've had planes show enroute when they were in the hangar. It's just a glitch in the faa computer from which flightaware and others get their data."


text:
Do solid-state flight recorders use wear levelling?
Most newer aircraft, plus some retrofitted older aircraft, have flight recorders that use solid-state flash memory as their recording medium, instead of the magnetic-tape recorders previously used (or the even older metal-foil oscillographic FDRs).  This has many benefits (vastly greater storage capacity, much-improved crash-survivability, lower power requirements, greater reliability, etc.).
Solid-state devices generally use some form of wear levelling to prolong the lifetime of their flash memory, where the device distributes write operations throughout its flash so as to preferentially write to memory cells with fewer accumulated writes under their belts.  As flash-memory cells become unreliable after a certain number of writes or thereabouts, this helps keep any individual cell from running up against its limit too quickly, making the device as a whole last longer before it starts experiencing memory-cell failures; however, it also destroys the direct correspondence that would otherwise be present between the physical and logical locations of any particular piece of data:

(Image by Attie at Super User.)
As a result, the device, and its users, are totally dependent on the device's memory controller to remember what physical addresses map to what logical addresses and to translate between physical and logical addresses; if one were to look directly at the flash memory itself, one would see only meaningless gibberish.
In contrast, magnetic storage preserves the direct mapping of physical to logical addresses; tape stores its data in rigid sequential order by its very nature, while floppy and hard disks (not used in flight recorders due to the minuscule capacity of floppies, the unreliability of "superfloppy" formats such as zip drives, and the fragility of HDDs, but the closest magnetic-storage equivalent to an SSD), although they do fragment data throughout the disk (unless nothing is ever erased from the disk, in which case they record sequentially), do so far less than wear-levelled solid-state media (fragmenting only when a piece of data is too large to fit in its entirety in the chunk of available space at hand), and store the data necessary to reassemble these fragments in the filesystem itself.
As a result, even if a magnetic storage medium is physically fragmented by a violent impact and its recording mechanism totally destroyed, any data on the individual pieces of the storage medium can still mostly be recovered (albeit with great effort), whereas, if the memory controller of a wear-levelled solid-state recorder were destroyed by impact and the individual memory chips torn from the recorder, the loss of the memory controller's internal remapping table would render any attempts to directly read the memory chips futile, even if they survived completely intact.
A non-wear-levelled solid-state recorder, in contrast, would accumulate dead memory cells more quickly than a wear-levelled recorder (shortening the overall lifespan of the recorder's storage medium and requiring that it be overhauled more frequently to replace failed memory), but would preserve the direct mapping between physical and logical memory addresses, allowing meaningful data to be recovered from the memory chips even if the rest of the recorder were completely destroyed.
Given all this, do solid-state flight recorders use wear levelling like most solid-state storage devices do (increasing the recorder's lifespan at the expense of potentially rendering the stored data unrecoverable if the recorder's memory controller is destroyed), or do they forgo it (improving the chance of being able to recover data from a very severely damaged or partially-to-mostly-destroyed recorder, and accepting the resultant hit to the overall service life of the recorder's storage medium)?

1: Which was actually a step down from the older foil recorders, which lasted for many weeks before the foil ran out (although at the expense of only being able to record a single-digit number of parameters and not being useable for the CVR); additionally, since the foil couldn't be reused, one could potentially retrieve FDR data from even further back in time by burrowing through the operator's FDR-foil archive.

I would be surprised if flight recorders do employ wear-levelling. That technique is really only useful in a situation where some memory locations are undergoing significantly more write cycles than others. But flight recorders, by their very nature, record information cyclically.

The question is, where that table of mappings is stored. One of the obvious places to store it is to use part of the same memory chip, storing nothing in the controller.

@h22, there is nothing stopping you from writing a flash memory linearly just like a tape. Then it does not have any mapping table. I don't know whether they actually do that, but it would make most sense.

@h22, also, most embedded devices don't have special wear-levelling controllers, but use log-structured filesystems to avoid non-uniform wear. Wear-levelling is only used on memory cards and SSDs designed as drop-in replacement for spinning disks because the filesystems designed for spinning disks are particularly bad in this regard, FAT being the far worst.

I don't know what kind of memory is used in FDRs.  One type that would be great is Ferroelectric RAM (FRAM), which can have 10 trillion write cycle capability and not need battery backup to retain the data. 10^14.  One could write to 1 location once a second for 317 years before wearing it out.

Explain thyself, cowardly downvoter.

I have not worked on Flight Data Recorders specifically, but considering the format, sampling rate, and storage requirements, I would expect that no wear leveling is incorporated because it isn't necessary.
Data would be stored sequentially, and the only time data would need to be erased is when it needs to be overwritten due to the entire storage region being full (a circular buffer).


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Why weren’t large, high-power radial engines built to take advantage of the Meredith effect?
Most aircraft piston engines fall into two general categories:1

Radial engines (radials for short2) have their cylinders radiate out from the crankshaft in a star pattern; they tend to have a blunt, cylindrical nose shape, and are generally air-cooled.
Inline engines (inlines) have their cylinders all in a line along the crankshaft from front to back; they tend to adopt a more streamlined style of nose, and are almost always liquid-cooled.

As coolant, piping for same, and radiators tend to have positive mass[citation needed], and aircraft are typically operated in a positive gravity field[citation needed], the liquid-cooling system needed by most inlines imposes an unavoidable weight penalty; additionally, it makes these engines comparatively fragile compared to air-cooled radials of similar size, as the whole engine can easily be disabled by a leaky coolant line.3
However, even though the radiator, by its very nature, has to stick out into the airstream in order to lose heat to said ambient airstream, it does not (necessarily) impose a drag penalty; in the process of being cooled by the ambient air, it transfers thermal energy to said air, and some clever mad scientists figured out how to use this to generate thrust, essentially turning the radiator into a primitive jet engine.  The thrust generated by this process (known as the Meredith effect) can easily exceed the drag produced by the radiator, turning the radiator into a net thrust producer; back when fighter aircraft still used pistons and props, this gave inline-powered fighters a performance advantage over their radial-powered counterparts, which is why most of the really successful piston fighters of World War II used liquid-cooled inline engines.  (Today’s inline-powered aircraft, which generally do not have a need to outrun pursuing fighters, make do with simple non-thrust-producing radiators.)
There doesn’t seem to be any reason why a properly-designed radial couldn’t benefit from the Meredith effect as well; indeed, it should work somewhat better with an air-cooled radial, since the thrust-producing air is being heated by the cylinders directly, cutting out the liquid middleman and one of the two efficiency-robbing energy transfers necessary in a liquid-cooled system.  Yet, despite this, and the fact that these big radials were used to power heavy aircraft that needed every bit of thrust they could possibly get, and the fact that the wide, flat, blunt nose of a radial engine makes the drag problem especially acute (and, thus, any possible way of reducing drag all the more desirable), none of the big radials ever was designed to take advantage of the Meredith effect.4
Why not?

1: In practice, so as to pack lots of cylinders into the smallest possible space, the larger engines from both groups tend to fall closer towards the middle; all but the smallest post-World-War-I radials have at least two to four rows of cylinders, stacked one in front of another, while most midsize-and-larger inlines have multiple parallel cylinder banks (again, usually from two to four).
2: No relation to the kind of radials you navigate with, except insofar as they both pertain to aviation.
3: This is one of the big reasons why all the really big World-War-II-and-later aircraft piston engines (the ones powering the big bombers of the war and the big propliners of the decade following it) were radials.  Big piston engines are unreliable enough on their own; trying to keep a really big liquid-cooled inline running would be an absolute nightmare.
4: You sometimes hear that the NACA cowling design used on essentially all post-mid-1930s radials was designed to produce extra thrust from the heated cooling air.  This is a misconception.  Although the NACA cowling did indeed reduce (and quite dramatically, too) the drag penalty of a radial engine, it did this solely by smoothing the rough aerodynamic lines of the uncowled radial; no Meredith-effect wizardry was involved.
Note: Not a duplicate of this other question.  That one asks whether radials used the Meredith effect; this one asks why they didn't.

@ymb1: The misconception, as it says right in your quotation, is that it would be more effective because the fins of an air-cooled radial are hotter than the radiator of a liquid-cooled inline, not that it would be more effective because of the reduced number of efficiency-draining energy-transfer steps (the justification that actually makes sense).  Also, the page cited by that quote merely states the same information as is in the quote, without providing any explanation of any sort.

I don't think you need a citation to back your assertion that liquid cooling components have positive mass.  Most of us are smart enough to realized this intuitively...

I have to endure too much lawyer-speak already at work, so please try to write more in vernacular.

There have been a number of inline air cooled engines, and by quantity manufactured, horizontally opposed engines (like the Lycoming and Continental engines found in light planes) arguably hold the majority.

First of all, any radiator thrust is limited by the amount of ram pressure which can be achieved at the radiator entry. This is just 1.4 times ambient pressure at Mach 0.8, and then very little flow speed remains (which is good, because that limits internal losses in the radiator).
Next, the heat exchanger should cause as little drag as possible. A blunt cylinder head is not ideal and the lamellas of a classical radiator are much better.
This means in consequence that the radial should ideally have liquid cooling in order to take advantage of the Meredith effect, and then it doesn't matter much where the radiator is placed.
As an example: The Blohm & Voss 155, a high altitude derivative of the Me-109, was said to produce most of its thrust with its wing-mounted radiators when flying at its operating altitude of up to 17.000 meters. The high flight Mach number there hurt propeller thrust but helped the radiator to take over.

BV 155 under construction (image source). The long pipe at the side of the fuselage feeds the turbocharger in the rear fuselage with engine exhaust gasses.

Compared to a turbojet engine, the heating (from cylinder fins) of the working fluid (air) in an radial engine is relatively small, and so will be the possible thrust augmentation via the Meredith effect.
Better results can be had by dumping the engine exhaust into the cooling air stream exiting the engine, and directing this blend of spent engine cooling air and hot exhaust gas into a rearward-facing exhaust nozzle- as used in the Convair 440, which had radial engines.
The utility of the liquid-cooled vee engine was well-established in ground vehicle practice before migrating the design into aircraft use. The outstanding advantages in aircraft applications were 1) minimization of frontal area drag by stacking the cylinders behind each other, which was enabled by liquid cooling, and 2) superior cooling of the cylinder heads and exhaust valves by routing the coolant passages around the valve seats and combustion chambers, allowing higher power output without relying on a rich mixture to carry away engine heat, as radial engines were forced to do.
Whatever weight penalty might have come with liquid cooling was amply compensated for by profile drag minimization. If you have data on survivability differences between liquid cooled vee engines and air-cooled radials subject to aerial machine gun fire, please share it with us here.
As an aside, consider that for the purposes of a maximum-power, minimum drag engine installation, all the engine manufacturers (American, British, Italian, Russian, German) that built liquid-cooled aircraft engines in WWII converged on the same basic and robust (and very successful) design solution: 60 degree vee, 12 cylinders, liquid cooled, pushrod-actuated valves, 1700 to 2000 cubic inch displacement.
Regarding heat transfer, the efficiency of heat transfer using pumped water-based liquids far exceeds that of using air as a heat transfer medium. The most critical design issue in this realm is not heat transfer inefficiencies in the engine-to-coolant step or coolant-to radiator step but the aerodynamic design of the air intake and transport ducting for the radiator, to minimize drag across all flight regimes.

Dont't forget that coolant pressurisation makes it possible to remove the same amount of heat even as air pressure drops with altitude. Of course, now the radiator has to be matched to the reduced air density. But the advantage is that supercharged, water-cooled engines can be cooled over the full altitude range whereas supercharged, air-cooled radials will develop cooling problems as altitude increases.

1) For any thermal engine, energy efficiency is directly correlated to temperature, while power density is indirectly correlated to temperature as well. Because radiator temperature isn't very high, a jet engine using radiator heat is very inefficient and bulky.
2) For a ICE engine, majority of waste heat is carried away by the exhaust so amount of energy available at radiator is relatively small.
3) The reason why Meredith effect works better for liquid cooled engine is, it's easier to concentrate heat into a small flow, hence raising operating temperature. On a radial engine this is near impossible.

The principle in general is known as the thermal ramjet: pass the air through a specially-shaped duct and heat it on its way through.
The Meredith effect applies specifically to intermediate circulatory systems which pump a special coolant fluid around in order to heat the air. Inline engines benefit from such systems because most cylinders cannot receive enough airflow and need a pumped coolant to collect the heat.
Radial engines have enough exposure and use the passing air directly as their coolant fluid. Their cowlings are indeed designed as thermal ramjets. If you look closely at the rear of the cowling, you can often see variable exhaust flaps similar to those on Meredith radiators.


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How big does an object in one of the ILS critical areas have to be to cause a problem?
ILS installations have a critical area extending some distance back from the glideslope antenna (primarily due to most glideslope transmitters’ needing to bounce one of their two beams off the ground in this area); objects or vehicles within this critical area can cause large variations in glideslope transmissions, potentially resulting in approaching aircraft being guided dangerously low above terrain and/or other obstacles.  A second critical area exists along the runway itself, where the presence of objects or vehicles can distort or scatter the the localiser beam, potentially causing dangerous lateral-guidance anomalies for approaching aircraft.1  This means that the ILS critical areas must be kept clear and unobstructed at all costs when an aircraft is performing an ILS approach, especially if visibility is low enough for aircraft to be reliant on the ILS all the way down to the runway (which simultaneously worsens the potential consequences of ILS-signal interference, as there is much less margin for error close to the ground, and makes guidance anomalies less likely to be detected immediately, as the pilots have little or no external visual reference with which to crosscheck the received ILS signals, and - unlike with higher-visibility approaches - will generally not be controlling the aircraft themselves, but, rather, monitoring the autopilot as it flies the aircraft down [human reaction times being far too long, and human control inputs far too rough and imprecise, to safely fly the aircraft all the way down to the runway without actual or simulated external reference]).
This raises the question of how big an object in the localiser or glideslope critical area has to be in order to cause significant distortion or interference to the ILS signals.  Obviously, tiny objects such as bumblebees or snowflakes are not large enough to have a significant impact (otherwise, most ILSs would be near-permanently useless due to insect and precipitation interference); equally-obviously, large vehicles like snowplows and eighteen-wheelers and 777s are (otherwise, there would be no need to restrict operations of these vehicles in the ILS critical areas,2 or to restrict ILS approaches while these vehicles are present within one of the critical areas).  But just how small does an object have to get before it no longer poses a threat - would a deer running across the departure end of the runway cause problems,3 or would it only be large enough to cause problems if it were in the glideslope critical area,4 or not even there?  What about an eagle (no, not this one) perched on one of the glideslope (or localiser!) antennae, or a robin flying around them?6

1: The localiser critical area is separate from the glideslope critical area because the localiser antenna is (usually) located along the extended centreline beyond the departure (far) end of the runway (allowing it to provide lateral guidance all the way down through touchdown and rollout), while the glideslope antennae are located alongside the approach (near) end (as we are trying to guide the aircraft to a touchdown in the first portion of the runway, not the last).
2: Aside, of course, from the restrictions inherent to all vehicle operations near active runways, ILS or no.
3: Granted, a deer running across any part of an active runway would almost certainly cause problems (likely in multiple ways), but let’s restrict ourselves to discussing its impact (if any) on that runway’s ILS signals.
4: Localisers transmit in the 108-112-MHz band, near the middle of the VHF range and sandwiched between the FM broadcast band (88-108 MHz) and the VOR band (112-118 MHz), while glideslope transmitters operate in a much higher frequency band (328.6-335.4 MHz, in the lower portion of the UHF range and occupying a slot dividing the 225-328.6-MHz and 335.4-400-MHz bands used for military-aircraft radiocommunications); hence, the critical size for interference with glideslope signals should be about a third of the critical size for localiser signals.5
5: On the plus side (for the glideslope), this also means that the optimal antenna size for a glideslope transmitter is approximately one-third of that for a localiser transmitter, allowing the former to use smaller, cheaper, lighter, easier-to-handle-and-support-and-replace antennae than the latter.
6: I am well aware that birds and aircraft do not mix; however, as with the deer making an uncleared runway crossing, my concern here is limited to their potential effects on ILS transmissions.


text:
Why does the FAA ban preboarding passengers from sitting in emergency-exit rows?
Of the several restrictions every U.S. airline passenger knows about regarding who can and can’t sit in an aircraft’s emergency-exit rows (no one under 15, or physically disabled, or travelling with small children, yadda yadda yadda), one of the strangest is a blanket prohibition against preboarders sitting in exit rows.
Now, this does make sense for some specific subsets of preboarders; for instance, one common category of passengers allowed to preboard comprises those with physical disabilities severe enough for them to require extra time, and a near-empty aircraft, in order to board (if someone is disabled enough to severely impair their ability to board the aircraft, one would probably not want to have to rely on them to potentially have to open and maneouvre a heavy emergency exit hatch), while another common preboarding group, families travelling with small children, is already excluded by the prohibition from exit-row seating of small children and those travelling with same.
However, the severely-physically-disabled and the possessed-of-small-children are far from the only types of preboarders; a third group of passengers routinely afforded preboarding rights by most airlines are active-duty military personnel, who are among the best possible choices for exit-row duty, due to their generally-excellent physical condition and discipline.  So why does the FAA ban preboarders as a whole from sitting in emergency-exit rows, rather than only those preboarders whose reasons for preboarding would actually impair their ability to perform emergency-exit tasks in an emergency?

As best I can tell, exit row seating is now nothing more than a revenue generating feature and your abilities to actually serve in the role aren't questioned as proved by the fact that you can reserve those seats online.

Can you point to the actual FAR that bans this? I cant seem to find it. 121.585 does not mention this and a lot seems to be up to the approved OpSpecs of the 121 operator.

I don’t think there is a specific ban on pre-boarders. More than likely, it’s a policy. It is probably per airline SOP. I frequently get the exit row. I either reserve it or get at check in. As far as it being a revenue generator, I don’t pay for it. Try to always fly the same airline. After a while, you get perks. If that is not a possibility, just be nice to your gate agent. Smiles are great currency. I have been denied reserving the exit row on flights on airlines I don’t usually frequent. That is where the smile comes in handy.

Evacuation can occur during boarding.  In this case, it may help if there are fewer people in the exit row.

Are you talking about Southwest Airlines? AFAIK, they're the only ones that don't have pre-assigned seats.

What makes you think this is a blanket rule from the FAA? Do you have a source you can share?


text:
Why does the A330 sit nose-down on the ground?
The passenger versions of the A330 have a small but noticeable nose-down angle when sitting on the ground:

(Image by contri at Flickr, via russavia at Wikimedia Commons.)
In contrast, A330s built as freighters have a noticeable bump under the nose,1 which allows the nose gear to be mounted low enough down that it reaches the ground with the aircraft sitting level:

(Image originally by Ceecookie at Wikipedia, via Leptictidium at Wikimedia Commons; cropped and modified by me.)
I can think of some disadvantages of having a nose-down body angle on the ground:

Boarding (and, to a lesser extent, deboarding) would be slowed down slightly by the passengers having to negotiate a sloped cabin floor (especially those having to drag very heavy pieces of luggage uphill in the process).
Ground servicing of cabin equipment would be expected to be made somewhat trickier by the sloped floor (a galley cart or other rollable object inadvertently left unattended for a moment would roll away towards the cockpit, potentially causing damage or injury if it has a sufficient length of unobstructed aisle to get up to a good clip).
The nose-down body angle tilts the aircraft forwards compared to the situation that would arise with a completely-level fuselage; this moves the aircraft's center of mass forwards, shifting more weight to the nose gear that would otherwise be carried by the main gear, and, thus:

Requiring a heavier, more substantial nose gear than would otherwise be the case.
Reducing the maximum braking force available from the main gear (and thereby increasing the aircraft's stopping distance).
Slightly decreasing the aircraft's directional stability on the ground (ye olde wheelbarrowe effect).

Indeed, the vast majority of large airliners sit level on the ground, rather than nose-down, so why is the A330 different in this regard?

1: Freighter A330s converted from passenger aircraft have no such bump, as the aircraft's cargo-loading system is fully capable of dealing with the slight slope.

I would assume that if the aircraft is designed to sit nose-down, they would design it to prevent the issues in your last point about center of gravity.

Cant answer your question but to add to the question.. the cabin floor also raises towards the rear of the aircraft. If you look at the window line just a bit forward of the last passenger door you will see a point where it slops upwards.

For one reason or another, the main gear was made longer that originally planned and it was decided to avoid the cost and weight also extending the nose gear to match. The nose down angle while rolling along the ground is no big deal one way or the other, except for looking bad and disconcerting passengers who wonder why the plane is tilted forward.
Lots of airplanes are like that, sometimes because of changes made during development, but more typically after fuselage stretches where the main gear had to be made longer to keep the extended tail off the ground during rotation (the flying pencil CRJ1000, which I used to be type rated on, feels like a backwards taildragger in that regard).  Obviously, the freighter needs a level cabin floor for loading, hence the nose gear band-aid; for the passenger versions, it's not really necessary and the blister and extra structure to do all that is just ballast and drag, serving no useful purpose.

It does not seem to come from a stretched variant. All A330 variants (except the -200F) have a lower nose (see page 60ff. in this PDF).

I fail to see how it answers the question ("why..."). You may explicit and highlight this point in your answer

I think this does answer the question. Main gear length is determined by the need for tail clearance at take-off and landing. Nose gear length can be anything you want (unless it's a freighter), and a shorter nose gear will be lighter, so relatively long aircraft end up with a nose down angle on the ground.

Edits made to flesh it out a bit.


text:
Why don't multiengine aircraft have to demonstrate spin recoverability?
(Building off this earlier question about spin-testing airliners.)
For normal-category aircraft1 in the U.S. (at least), only single-engine (or, in the case of some gliders, no-engine) airplanes need to demonstrate the ability to recover from a one-turn (or, if the aircraft is intended to be certified for intentional spinning, six-turn) spin.  This means that, for instance, the single-engine Cessna 208 (MTOW 3630 kg) has to be successfully recovered from a one-turn spin, whereas the much-smaller Piper PA-34 (MTOW 2155 kg) is exempt from this requirement solely by virtue of having a second engine.
There is nothing about multiengine aircraft that makes them inherently resistant to spinning compared to single-engine aircraft; indeed, if anything, it would be expected to make spins somewhat more likely (think "aftermath of botched or absent pilot response to an asymmetrical engine failure"2).  If, instead, the number of engines is being used as a proxy for the size and intended audience of the aircraft (as suggested in this comment on the aforelinked question), then I don't see any reason not to simply use a dividing line based directly on weight (especially since, as noted above, there are many large single-engine airplanes and small multiengine airplanes).3
Given all this, why aren't multiengine airplanes (especially small multiengine airplanes, such as the aforementioned PA-34) required to demonstrate spin recovery like their single-engined compatriots are?

1: Utility and aerobatic airplanes do have to demonstrate spin recoverability even if they have more than one engine.
2: Especially for multiengine tractor-propeller aircraft with wing-mounted engines, where, when flying at very low airspeeds, simply shutting down one engine or losing it to a mechanical failure can be enough to immediately stall its respective wing (due to said wing losing the air previously being blown over it at high speed by said engine's propeller).
3: Granted, even large multiengine airliners can find themselves spinning on occasion, something that (inadvertently) happened to (for instance) the first 307 and the first 737;4 however, I accept that an airplane requiring an ATPL and a specific type rating, not to mention a second pilot, is (by virtue of hopefully-good piloting) rather less likely (barring a major structural failure) to be placed in a spin than one requiring merely a PPL, and also that very large aircraft such as these are likely to become debris clouds if spun.
4: For the record, both the Stratoliner and the 737 were successfully recovered from their spins, although the former then almost immediately disintegrated in flight due to an overly-aggressive pullout from the subsequent dive.5
5: Hey, I can nest footnotes!

Because it would impose severe constraints on their design.
Factors such as mass distribution make many twin-engine and multi-engine aircraft inherently resistant to spin recovery, despite the large rudder or large rudder moment-arm that is often present on these aircraft.  In many cases these aircraft are prone to flat spins.  Also, during the recovery from a nose-down spin, a large aircraft may exceed Vne before pulling out of the resulting dive, or may be overstressed during the pull-out.  In the real world, a pilot should avoid spinning a typical twin-engine or multi-engine aircraft, because recovery might not be possible.
"No multiengine airplane is approved for spins, and their spin recovery characteristics are generally very poor."
-- from https://www.flightliteracy.com/stalls-in-multiengine-aircraft/
Related questions on ASE:
Is spin recovery possible in an airliner?
Why aren't airliners spin-tested?
Other related links:
https://www.flightliteracy.com/stalls-in-multiengine-aircraft/
https://www.pprune.org/flight-testing/226351-spinning-airliner.html
https://www.airlinepilotforums.com/hangar-talk/6370-spinning-airliner.html
google "spin recovery twin" or ("multi") for much more

Many other relevant links could undoubtedly be added, including links specific to smaller twins.

The most common response I've been given is that the inertia developed with so much outboard mass cannot be overcome by the flight controls. That said, the Duchess was extensively spin tested and found to be recoverable in established spins. My guess is recovery would be unique to each design based on power plant location and mass, rudder design, and left vs. right hand spinning (excluding counter-rotating designs).

Welcome. Please note that we expect facts from answers, not guesses - this requires links or fact-based detail.

I can only speculate on why the FAA does not require it since I don't know their reasoning. Here is why I don't think it is necessary:
The primary tool to stop an aircraft from spinning is the rudder:

Power to idle
  Ailerons neutral
Rudder opposite the spin until rotation stops
  Elevator forward to break the stall

(What is the Beggs/Mueller emergency spin recovery technique?)
In a single engine aircraft, the spin recovery needs to be demonstrated because the rudder might otherwise not be sized to be able to stop the spin. It would only be large enough to provide lateral control during takeoff and landing as well as coordinate turns in flight. Full rudder will never be used except for spin recovery, so this becomes the dominating factor.
On multi-engine aircraft, the rudder must be sized to compensate asymmetrical thrust in case of an engine failure. This limits the takeoff performance via $V_\text{mcg}$ (Are there any aircraft where minimum-V1 is limited by Vmcg?). The rudder will therefore already be sized large enough and spin recovery is no longer the dominating factor determining the required size of the rudder. I assume that is why it does not need to be demonstrated.

This makes me wonder about the Cessna Skymaster, with two coaxial engines. Did (or would) it need to demonstrate spin recovery, since engine failures on that one don't produce asymmetrical thrust?

Full rudder will never be used except for -- cross-controlled sideslips -- and spin recovery.  Many pilots have experienced running out of rudder authority when landing in a strong crosswind.  See various comments on Zenair aircraft with all-moving vertical tail elsewhere on ASE.

@TerranSwett that's an interesting example, I don't know if that one was spin recovery tested or whether or not is should be...

As you can see by my answer, I don't think this answer is very accurate :(


text:
Why are the angle-of-attack sensors on most airplanes mounted on the forward fuselage rather than at the wing roots?
A source of reliable angle-of-attack information is important for airplanes, as flight at an excessively-high angle of attack can cause the airplane to stall, which is generally considered to be an undesirable occurrence.  To this end, airplanes generally have several redundant angle-of-attack sensors (usually consisting of vanes that stick out into, and align themselves with, the airflow, but sometimes using complicated pressure-sensing mechanisms instead) to provide warning of a dangerously-high angle of attack.
These sensors, however, are generally mounted on the forward fuselage, below the cockpit, which is not, for most airplanes, where high angles of attack actually cause problems.  Where AoA matters is on the wings, which produce the lion’s share of the airplane’s lift and which need to be kept from stalling, and where the direction of the local airflow is not necessarily the same as that experienced by the AoA sensors on the forward fuselage.  Exactly how not-same it is depends (as do quite a lot of an airplane’s aerodynamic properties) on the airplane’s airspeed, which is why readings from nose-mounted attack-angle sensors need to be adjusted to correct for the effects of airspeed, which is why (for instance) high-attack-angle protection on fly-by-wire Airbusses is inoperative in the absence of valid airspeed data.
Mounting the angle-of-attack sensors at the airplane’s wing roots, rather than beneath the cockpit, would allow the AoA to be measured directly right where it counts, eliminating the need to correct their readings for airspeed and allowing accurate attack-angle measurement even without any airspeed information at all, so why do most airplanes still have their attack-angle sensors on the forward fuselage instead of the wing roots?

Are you aware of any situation where the AOA measured at the wing root is different from the AOA measured at the cockpit, or a situation where that difference matters in a beneficial way?

@GalacticCowboy Depends how bendy the wings/fuselage are, and therefore whether the AoA measured at the wings could be significantly different from the measurement at the nose.  Then again the AoA at the wing root wouldn't change as the wings bend up/down, it would change most out at the tips.

Would installing the AOA vane (or, in general, sensor) at the wing root be more accurate than installing it near the nose? No, it wouldn't. In fact, it may be slightly worse due to the larger upwash at the wing leading edge and the vane protrusion may even negatively interfere with the wing aerodynamics.
Traditionally, AOA measurements are used for stall warning and, if required, stick pusher. During flight tests, the thresholds for stall warning activation (and stick pusher activation) were calibrated to the local AOA measurements from the vanes to satisfy the certification requirements, while minimizing $V_S$/$V_{SR}$ to maximize performance.
In FBW aircraft, if the control laws have AOA dependency, the control law would typically be designed with aircraft AOA (a.k.a free-stream AOA) as specified in wind tunnel and/or CFD. Therefore, the local AOA measurements would need to be corrected to the aircraft AOA before being consumed by the control laws. Answer to this question outlines the methods for such correction during flight test.
Addendum:
There are a number of other AOA measurement devices besides vane and Smart Probe (used on A220 and E170, E190). The most common ones are leading edge orifices or tabs used on GA aircraft (thanks @JanHudec for pointing out). These operate by sensing the movement of the stagnation point as AOA increases. The downside, of course, is that the stagnation point associated with the required margin to stall is different at varying Mach numbers and across high lift configurations.
This NACA report contains a number of wing-mounted stall warning devices tested in the last century.

In large aircraft, the AoA vane is installed that way. But all small aircraft sense the position of the stagnation point directly on the leading edge with either small vane (triggers stall warning if blown up) or a pair of ports (in some cases even purely mechanically—there is a whistle in the connecting pipe that sounds if air flows up). That does not give AoA, just stall warning, but is simpler.

@JanHudec Very good information. Are these devices nice-to-have, or are some of them needed to meet 23.207?

When the aircraft does not have AoA vane (most small GA aircraft don't) and need stall warning for 23.207 (sometimes the stall buffer is enough), it is needed for compliance. But it is on straight untwisted wings; on twisted swept wings it might be harder (or too hard; on swept wing it will be severely affected by side-slip) to calibrate.

"In FBW aircraft, if the control laws have AOA dependency, the control law would typically be designed with aircraft AOA (a.k.a free-stream AOA) as specified in wind tunnel and/or CFD."  Why are the flight-control laws of fly-by-wire aircraft dependent on freestream AoA, rather than on wing AoA, given that (for aircraft that produce lift with their wings) what actually matters for the aircraft's flight characteristics is the wing AoA, not the freestream AoA?

@Sean You could identify stall boundary using AOA measured close to wing. But FBW laws are model based, and the development models are inevitably constructed from CFD and tunnel data, where it's much easier to specify freestream AOA.

Mounting the AoA sensor at the wing root indeed makes sense if spurious effects occur, such as rapid dynamic effects or non-linearities. The AoA measurement is pretty straightforward in the linear area of the flight envelope, below stall AoA, and in this area the best place for mounting the AoA sensor is in a relatively undisturbed place which makes it simpler to calibrate during flight tests. As has been done for decades.
However, times have changed, there are new requirements mandating recovery from a fully developed stall, not a linear region. New requirements on measuring AoA and stall separation may follow...

What you will see soon is a development of something based on the "Smart Boom" which is used on the latest test programs and dispenses with physical vanes and just uses ports at various locations at the tip of the boom to measure pressure and software calculates AOA.  You'll see something like a small blister on each side of the nose with holes all over it, replacing the vane.

@JohnK: By that logic, wouldn't you want those pressure sensors on the wings themselves? After all, air pressure on the wings is directly what keeps an airplane in the air.

@MSalters Smart Probes also serve as airspeed sources. You wouldn't want them to be near the wing due to upwash.

@Jimmy I think MSalters' point was: pressure sensors should directly determine if there's a stall ongoing, in situ as it were, without even needing any proxies (airspeed and/or AOA).

@leftaroundabout In order for this to work, you'd need pressure sensors everywhere on the wing (what if stall occurs mid wing from TE, vs stall occurring near root at LE due to icing for instance).

@Jimmy yes – but pressure sensors are small, lightweight and cheap (unlike AOA vanes), so it would seem plausible enough to just spread 100 of them or so all over the wing.

@leftaroundabout It's certainly plausible. But now you're replacing one redundant state estimation with N  coupled state estimations. It just screams complexity for very little gain (if any at all as addressed in my answer). AOA sensors have been working reliably for decades.

@Jimmy: True, but 7 fail out of a hundred you just shrug it off. Redundancy is a well-understood form of reliability. As for the "partial stalls over different parts of the wing", your AoA sensor can't deal with local icing at all.


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How does one reverse direction on a VOR radial?
Tracking inbound, say on R-270, how do I track outbound on the same R-270? What intercept heading shall I fly?

Well, make a 180 degree turn, plus however much more seems appropriate to get back onto the radial. The bigger the intercept angle, the sooner you'll rejoin the radial, but also the greater the chance of overshooting through it. Farther from the station, the 180 will take you fewer radials off the 270R, but the same cross track distance. An intercept of 10 to 30 degrees would generally work fine.

It sounds like you're describing a procedure turn?

Very much related: https://aviation.stackexchange.com/questions/53981/how-do-i-determine-which-radial-intercept-angle-to-use

Spin the obs 180 so it changes from "To" to "from" then make a 210-220 degree turn(180 plus a 30-40deg intercept) and fly until the VOR radial comes in, then track the VOR.


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What is Arctic Control Area (ACA)?
I saw that in Jeppesen airway manual but I didn't find a definition for it. What is that?
How to establish it? Who establishes it and for what reason?

from
http://code7700.com/high_latitude.htm
Apparently defined by Transport Canada:
https://www.tc.gc.ca/media/documents/ca-publications/AIM-2018-1-E-ACCESS.pdf
page 192

Pondlife, how are you able to make the .png show up like that?

click 'edit' and study the changes.

@PeterKämpf to be precise they should click "edited X hours ago"

@Federico: That is even better, agreed. I learned MathML by clicking 'edit' on posts where I wondered "how the heck did they do this?"


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How can I decode Lycoming engine number?
How can I decode Lycoming engine number suffices?
What does D3G mean in o-320-D3G or D2A in o-320-D2A?
Is there any chart or tabel for decode suffixes?

I got the following information for this website:

Also if you scroll down here you can see the model numbers that you talk about in your question.

The last character seems to be an indication of the variant of the engine as shown in the document.  The D indicates Dual Magnetos and the 2 or 3 seems to indicate some type of counterweight application.

This PDF on Lycoming's web site covers it. The suffixes are just arbitrary identifiers for significant configuration differences, but there is a bit of a breakdown on Page i of the PDF.  Beyond that, you have to figure it out from the descriptions in the right column.  If you study them the logic should start to emerge.

He didn't say about suffixes that's my problem

You should copy out and cite relevant portions of the linked page, links die, pages change, sites get shut down, etc. "Link only" answers are very much discouraged.

He needs to see the entire document, not just a sample.  I changed the link to the root document on Lycoming's site.  That link shouldn't be going anywhere.

@JohnK that link went somewhere :)


text:
Could a larger consumer drone "take down" a passenger plane?
As a frequent flier, I'm just concerned about my own safety.
Could a larger consumer drone, such as DJI Inspire, (intentionally) "take down" a passenger plane?
When I say take down I mean causing the plane to crash or emergency land.
I guess just a contact would not do too much harm but could it do some when flying in the engine?
Considering that larger drones can easily carry bigger cameras, it could also carry a 1kg or similar of explosives.
Are drones the biggest threat to commercial airlines as anyone can buy them and the chance of finding the pilot is very small?

Just a comment, but I firmly believe, at least in the US, this would happen exactly once. As soon as it was proven to have been a drone that was used, all drones flown privately would be grounded and controlled in some fashion as to make their continued use by private or commercial entities impractical/illegal.

There are cases that may be really dangerous, e.g. losing an engine when landing, so close to the ground, that there is no time for the crew and the aircraft to react. The EU (EASA) is preparing a regulation where all drones will be sending an individual ID, like a transponder. Unidentified drones will then be considered unfriendly, and likely destroyed (or captured) by another drone. This regulation also creates three categories of hazard. That said (today) drones are less a problem than birds, which already caused crashes.

I think this is likely that it could in some weird fringe edge case but with all the restrictions and precautions around their use I cannot see a scenario where this would. I mean for starters the construction of almost any drone barely could survive a rough landing even a high quality drone like a dji still will just shatter if hit right.

Note that "emergency landing" doesn't have to mean the plane is crippled. You might consider Swissair Flight 111; they were descending for an emergency landing long before actually declaring an emergency (though they did declare a situation of urgency). That particular flight ultimately crashed, but many urgency and even a substantial number of emergency situations end with no casualties and minimal additional damage (beyond what caused the urgency/emergency situation to begin with) to the aircraft.

Airliner can usually take a hit of something like the size of a turkey and consumer drones isn't much smaller than that.

@user3528438 the OP mentioned that the UAV might carry a payload, and some drones can pull up to 7 kg. I'm pretty sure that an IED of that mass would pose a significant danger to an airliner.

If your definition of drone is any remote control aircraft freely available to consumers, then the answer is yes, but highly unlikely.

Its very unlikely, but it is possible. First, I'd like to point out that Radio Controlled Aircraft (RC Aircraft) have been available to consumers since at least the late 1950s. Hobbists build RC aircraft all the time, and when I was a kid I built my own RC aircraft that was much bigger than most commercially available "drones". To focus on drones alone misses a big slice of the pie. RC aircraft are sometimes built as 1/4 scale models of the original aircraft and can weigh 100lbs or more, so imagine a remote control aircraft that is 25% the size of the real aircraft.
So, the potential has always been there for at least the last half a century for a remote control aircraft to have enough mass to potentially cause a serious collision with a real aircraft. Imagine if a couple of 18lbs geese took down  Flight 1549, what would a 100+lbs quarter scale RC Aircraft do.
Personally, I've never been too concerned with this because I've flown both RC aircraft and real aircraft. It would be extremely hard for a drone or RC aircraft pilot to target an aircraft and hit it in its most vulnerable locations such as cockpit or engines.
So, yes, its possible, but I would not lose any sleep over it.

Comparing RC model and quadcopters in the context of the question seems curious. RC model pilots have usually a certain knowledge and ethic. They are welcome, at least in my country, within aerodromes limits where they have their protected area and can gather and fly. Quadcopters can be bought at Wallmart or Lidl by anybody, who can charge them and fly within the next hour, alone, and without knowledge of anything.

@mins you make valid points. My point is that "drones" are just high tech versions of RC aircraft that have been around for 50 years. While its true that most RC pilots have certain knowledge and ethics, there is no requirement to have ethics or certain knowledge in order to buy a large RC aircraft. As early as the 90ies, there were pre-fab RC aircraft that were "Ready-to-Fly" out of the box that were much bigger than most of the quadcopters available today. Your point that quadcopters can be flying within an hour of purchase by anyone is important, and its why "drones" have become a problem.

@Devil07 Also, most drones come with sophisticated flight control systems, and most RC aircraft don’t (because where’s the fun in that!). Plus, drones (the ubiquitous type) can hover, and the RC 747 can’t. This means, unfortunately, it is much easier to get a modern drone stationary into the ILS glide path for that million-clicks-photo than to fly a photo pass with the hand flown RC 747. While potential damage is much higher in latter scenario, probability of the former is even greater...

@mins I think the OP question is more about hostile intentions, and from that point anyone with hostile intentions could take a rc craft


text:
Who checks that pilots have their licenses?
One weird thing came to my head In the ground, Every time you drive an 91 CRX SIR/Civic Si EM1 or ride an Honda Dirtbike There is an possibility of getting busted by the cops waiting in the temporary checkpoints But what about the air? Who will check (Non existent) licenses of DC-3/Bell 47GH pilots?
Who will check (Non existent) licenses of C208B Grand Caravan Amphibian pilots on the sea? Who will check people that flies alone in a Learjet 35 during IFR conditions? (I know, there are countries that you can do IFR flights alone)
Do you tell your license information to the ATC before the takeoff or there is an another way like authorities requesting flight logs of an C208B etc?

Just as people can go for quite a while driving without a license before they get caught, there is no certain way to catch somebody who goes flying without a license.  There are various ways that it can happen, but none of them are certain.
There was a quip quoted elsewhere referring to the high proportion of unlicensed pilots in Alaska, that supposedly the FAA had a goal of getting at least half of them licensed.  I have no idea how much, if any, truth is behind that statement.
On the other hand, just as having a license can make various things you might do with a car easier or possible, there are plenty of instances where having a pilot license is necessary:

Renting a plane
Buying insurance for a plane you own (without a convincing story of who else would be flying it, at least)
A "ramp check" by an FAA inspector
Getting a job (from a reputable company, at least) as a pilot

If you file a flight plan for your flight (required for IFR -- mostly, not required but very highly recommended for VFR), part of that is to provide a name for the pilot.  But that's it, just a name, not a license number.  (Phone number, yes -- so they have somebody to call in case you're overdue so they can see if you simply forgot to close your flight plan.)  I don't know how often that info would be checked against any database of current pilots, but the potential would be there.  But the ways the FBI would find people in an investigation is wildly different from what's routinely done by Flight Service.
So if Farmer Joe (licensed) owns an airplane & his (unlicensed) brother Fred flies it every now and then from their private dirt strip, the chances of Fred getting caught are probably pretty slight, unless something goes pretty badly wrong.  And, depending on Joe and Fred's tolerance for risk, they might be entirely okay with that scenario.
Me personally, there's no *%#@ing way I'd be party to any such arrangement, but I'm probably more cautious than some Alaska bush pilots that way!  This thread discusses the consequences for flying without a license.

I've heard of the FAA conducting ramp checks but never experienced it myself.
I've only experienced being checked when there was an accident, and FAA was investigating
I've asked this same question of pilots in the past and gotten rather comical responses, like "as long as you don't crash the faa doesn't care" and things of that sort. Licensing is for knowledge, knowledge leads to safety for you, your passengers and those on the ground and their property. Small craft that don't do much damage don't require the license, part 103 for example

it depends on whether or not your plane carries hull insurance. No insurance underwriter is going to knowingly insure an aircraft given that its owner is unlicensed and pilots the craft. This means that the FAA might not care whether or not you have a license, but your insurance agent almost certainly will.


text:
Is it normal ops to dispatch an airplane after a stick shaker was on throughout the previous flight (Lion Air 610)?
I've been studying Figures 5 and 7 of the Lion Air interim report and cannot understand why the airplane was dispatched on the "Loss-of-control" flight when the Left stick-shaker was on throughout the entire previous flight (Figure 7). Can this occur in normal operations everywhere?
I have no experience with ground operations (just 35 years with design of flight control equipment), so I'm asking the airline folks here. (I understand that often multiple causes lead to a crash, so I'm looking for understanding, not blame.)

I'm voting to close this question as off-topic because it discusses an accident that is still under investigation.

Why is the AoA constant during climb and descent?

@Pheric in any non-accelerated flight situation (basically everything except initiating and ending a climb or descent, and turning) the AoA is only a function of airspeed, mass, flap deflection and air density. Since these factors remain roughly constant for most of climb and descent, so does the AoA.

Well, if the shaker was running abnormally like that, the crew would have done a QRH procedure, if any, for that condition, and reported the snag at the next stop, and something would have been done by maintenance to release the plane.  Like a part was changed, or the problem went away and couldn't be duplicated after a test was done on the ground, whatever was required to get a maintenance release.  It would have to have been released as serviceable, one way or another.

Very clear answer! You just taught me about QRH and I spotted a description at What exactly is a QRH Thanks.


text:
What are those arrow markings on the wing?
I recently flew on a Boeing 737-800 and found these arrow markings on the wing. What are they for?

These tell the air which way to go over the wing. - If the air goes the wrong way it makes the ride bumpy.

I love that this comment has 2x the upvotes of the correct answer!

They are the overwing exit markings. You can see them in full in the following photo.

Boeing 737 Max overwing exits. By Oleg V. Belyakov - http://spotters.net.ua/file/?id=110706&size=large, CC BY-SA 3.0, Linkec
This is because as already noted in another answer, B737 does not have self inflating slides for its overwing exits and as such, the passengers need some guidance for exiting, to prevent them from going the wrong way.

Pessini
The above image shows the procedure for using the overwing exit.

+1, but I'd add the following to make this answer 100% complete for my taste: (just nitpicking from the labels in the question) This is not really a feature related to the aircraft itself (Boeing 737-800), but a feature of the livery (the paintwork) put there by the operating company. The only requirement is that they must have emergency exits over the wings. E.g. I have seen these on A319 and A320 from companies like EasyJet and AerLingus

They direct people who've used the over-wing emergency exits to proceed to the back of the wing, where the flaps are (hopefully) extended, giving them something to slide down to get to the ground.  The leading edge would be a much harder trip down, AND if the engine is still running, you're about to run forward into the area where you're at risk of being sucked into the running engine.  If you went aft and get caught in the jet-blast, you may tumble, but that's better than hitting the spinning fan blades!

If one engine is still running you're unlikely to be disembarked on that side so that comment seems erroneous. Never heard of an evaluation with all engines running. Also the air flow out the back of an idling engine is still hot and powerful, I'd rather not get in its way.

@Notts90  There are many reasons you might need to evacuate, many of which have nothing to do with an emergency engine shutdown. From inside the cabin, one's ability to determine if a particular engine is or isn't running is a little limited - especially with smoke & panic in the cabin.The reason you don't hear of many evacuations with engines running is, it's a bad thing & pilots will try to get engines shut down before ordering the evacuation. But that's not certain to happen 100% of the time. Yes, jet blast is unpleasant, but far more survivable than going into the fan blades!

A powered down airplane is a lot quieter than you'd think, simply because a powered-up airplane is so loud.  Hard to experience the spookyquiet unless you're on a train when the power/HVAC goes out.

There have indeed been emergency landings where it's been impossible to shut down an engine (QF32 for example), nor can you usually see the engines from the cockpit if the instruments aren't accurate. In QF32's case, there was no need for an emergency evacuation, but had there been a serious fire on board there would have been no option other than to evac passengers with or without the engines safely shut down.


text:
How many wing attachment nuts are there on a DC-3/C-47?
How many wing attachment nuts are there on a DC-3/C-47? I once participated in putting one together and is now writing about it, but cannot remember how many nuts there are, only that it took forever to line them all up.

Welcome to aviation.stackexchange.com!


text:
Why are flying-boom tankers restricted to a single boom?
Tanker aircraft can use one or both of two refuelling systems:

Flying boom: A rigid boom is lowered from the tanker and inserted into a receptacle on the roof of the recipient aircraft.
Probe\drogue: A flexible hose with a (usually) canvas cone on the end is unreeled from the tanker, and the recipient aircraft flies a forward-pointing probe into the center of the cone.

Aircraft can have multiple drogue units...

...but are limited to a single boom.

What prevents a tanker aircraft from having two or more booms?

Which plane is it in the first image?

@HarshilSharma Victor tanker.

There are several reasons why it is hard to support multiple booms on a single tanker:
1) Booms need an operator who is located in the fuselage. Video systems provide for remote control on newer tankers, but older ones still use direct view or looking straight down the boom at the refueling point in the receiving aircraft.
2) The boom is physically large. Its weight, large diameter and telescoping tube length would be difficult to install on a wing.
3) A wing bounces around a lot more than the fuselage does. Since the boom is rigid, this complicates keeping a good connection.
4) The high flow rate of a boom is only useful for larger aircraft like bombers, which are too big for simultaneous refueling. This somewhat reduces the advantage of having multiple refueling points.
Probe and drogue has a lower flow rate through a lighter, narrower hose. It is passive from the tankers point of view, and it is flexible.

The Airbus A330 MRTT has had a remote control only boom in service for several years now, no need to wait for the KC-46.

Good catch. It looks like Airbus has also had some success demonstrating automatic receiver contact with the boom.

The KDC-10 and KC-767 also use remote controlled booms.


text:
Did the space shuttle have a stall warning system (such as a stick shaker)?
I've been wondering about this, but I can't find any sources one way or the other:
Was the space shuttle equipped with a stick shaker and\or other stall warning system?

Interesting question

I remember there was a movie where a shuttle stalled before any warning was given except one from a chase jet. But that's just a movie.

Hey, there was a little blinkie light that came on at 1:13 in https://youtu.be/rKHW39mShF4! Granted, it's not very specific.

The shuttle was not built with this capability. NASA AMES had a project MIDAS intended to improve the shuttle's cockpit information display and management. In its list of problems to address:

Finally, there is no warning or guidance/autopilot limiting when approaching a stall on entry.


text:
What are these silver stripes on Cosmic Girl for?
Cosmic Girl (a 747-400 used for launching things into space)1 has a network of silver-coloured stripes on its empennage, starting at the (closed-off) last cabin window, and going aftward and upward from there, with branches running onto, and up, the vertical tail; there also appears to be a similar stripe emanating from the (also-closed-off) third cabin window behind the second main-deck exit door and running downward onto the wing root:

(Image originally by Crishazzard at Wikimedia Commons; modified by me.)
What are these stripes for?

1: It actually had that name before it became a rocket launcher - it didn’t get it from Virgin Orbit.

Related to the fifth-engine-attachment-point-for-ferrying, which is the spacecraft attachment point now:  https://aviation.stackexchange.com/questions/24181/can-the-a380-ferry-an-extra-engine-like-the-747

It's aluminum "speed tape" being used to run wires around the outside of the fuselage, possibly for load cells or some other kind of sensor related to whatever is being tested and that was impractical to run internally.  If you zoom in the image and look carefully at the vertical strip to the right and below TEST, you can make out a dark line in the middle of the tape that is a shadow from the wire bulging out.  Strictly temporary.
It looks like two window panels have had their acrylic panes removed and replaced with aluminum blanking plates with holes for passing the wire out through the pressure hull, making it a simple job to return to the normal configuration.

For those wondering, no, speed tape isn't ordinary duct-tape. It's specialized duct-tape.

Speed tape is what ducks actually use...

It's not duct tape, which is plastic/fabric.  It's an extra heavy duty variant of the aluminum tape you get at the hardware store. Much thicker with a stronger adhesive.